When oil or gas is produced from a subsea well, various types of releasable connectors may be used to latch the control pod in place. Hydraulically controlled latchdown mechanisms enable the use of detachable and retrievable control pods so that the controlling equipment may be retrieved to the surface for repair, if required. Hydraulic fluid used for control passes between the tree or other subsea structure and the control pod, and complimentary fluid openings must be aligned and sealed.
The mating surfaces which define the complimentary fluid openings may be preloaded and held in firm contact against various loads which may occur in varying directions and magnitude. It is therefore desirable to secure the connection in a symmetrical pattern since loading may occur in any direction.
Various linkages to accomplish lockdown of control pods are shown in U.S. Pat. Nos. 3,701,549, 3,817,281, 3,840,071 and 4,648,629. Rather than use face seals on mating tapered surfaces to connect hydraulic and/or electrical lines, present day control pods preferably use hydraulic and/or electrical coupler halves which are secured to the lower plate of the control pod and the upper receptacle plate of the subsea oilfield structure, such as a tree, so that springs or other biasing elements in these connectors are compressed when the control pod is moved to its final position. U.S. Pat. No. 4,223,920 shows a lockdown using wedged dogs. Other relevant patents of interest illustrating subsea connections include U.S. Pat. Nos. 3,486,556, 4,611,831, 5,794,701, 6,017,065, and 6,471,250.
Most control pod latchdown mechanisms have disadvantages which have limited their acceptance, particularly in deep water. The mechanism which latches the pod to the subsea tree frequently is not visible by an ROV, thereby presenting difficulties with assuring that the pod is properly latched to the tree. Some pod latchdown mechanisms require both a reciprocal and a rotational actuation motion to latch the control pod in place, thereby complicating the latchdown procedure. Many control pod latchdown mechanisms are not designed to perform latchdown using the abilities of an ROV, and instead use an umbilical line to the surface. While some latchdown mechanisms provide a latchdown force sufficient to connect the hydraulic couplers, prior art latchdown mechanisms do not move the control pod to decouple the couplers during the release of the latchdown mechanism.
The disadvantages of the prior art are overcome by the present invention, and an improved control pod latchdown mechanism suitable for latching a control pod and related control lines to a subsea oilfield structure is hereafter disclosed.